Electromagnetic interference (EMI) is disturbance that can degrade or limit the performance of an electrical circuit affected by it. Sources of EMI that may affect a circuit include any object that carries rapidly changing electrical currents. Effectively immunizing a particular device from electromagnetic radiation from an external EMI source, and effectively avoiding damaging or undesirable radiation from a particular device, may require use of an EMI shield. That is, an EMI shield may serve one or both of two purposes: it may be installed over a particular component to shield that component from effects of radiation from external sources or it may be installed over a particular component to prevent radiation originating from the particular component to prevent it affecting surrounding components or devices.
Integrated circuit (IC) device components can be sources of unwanted electromagnetic signals. ICs as such are used in portable electronic devices such as cell phones, and in electronic equipment, including home entertainment equipment and computers. A portable electronic device such as a cell phone typically contains several IC components (which may be IC chips, IC chip packages, or IC package modules) coupled onto a circuit board, and some of these components may generate EM signals that interfere with the operation of other components in the device. EMI shielding may be required to protect circuitry in an electronic component from an external source to the component (including other electronic components).
In one approach to protecting components from EMI, shielding is constructed over the components. The shield is made of an electrically conductive material such as metal sheet (which may be perforated) or metal screen, electrically coupled to a reference potential, which may be ground, for example. It is typically formed as a box or cover installed over the component to be shielded and soldered to contact points on the substrate surrounding the component. Substrate can be such as circuit board. Alternatively, a frame may be soldered to contact points on the substrate, and a sheet metal cover may be snap-coupled to the frame over the component. Undesirably, such a shield adds weight and bulk (thickness, length and width) to the device in which it is used. This approach does not meet current thinner package requirements.
In another approach to constructing a shield, layers of material are applied onto the circuit board and the components by sputtering. Known problems relating the sputtering technique are 1) very low unit per hour (the device need to be sawed before sputtering and each target material needs a long sputtering time); 2) costs relating to the sputtering machine; single sputtering layer thickness is thin (<5 μm), and therefore, usually 2-3 sputtering layers are required; 3) marking related process issues (the laser mark is required before and after the sputtering, there remains some challenges of doing laser mark on the metal based sputtering materials).
Yet in another approach EMI shield is formed by application of the shield material where it is needed to provide the desired shielding effect. Accordingly, less shielding material is required, than would be deployed in a configuration in which the component is fully covered by the shielding material, or in a configuration in which the shield material is applied fully over a broad area including the components and then removed in part from areas where it is not needed, or otherwise to form openings (as in “subtractive” processes).
Yet in another approach the conductive material is coated outside of the device, either by spray coating on the single device external surface or by printing on the half diced package before sawing. Known problems relating to this approach are 1) uneaven coating thickness on the surface and side; 2) high risk of exposing on the package corner and no conductive adhesive coverage; 3) high risk of contamination and also leakage issue during manufacturing; 4) marking related process issue and same as sputtering process; 5) low unit per hour; and 6) high waste levels.
Furthermore, all current processes have some difficulties in the marking process. Currently available laser mark processes cannot be fully used for printing or spray coating types, due the fact that the conductive adhesive is mainly shinning and the mark is not clear. On the other hand for sputtering type, laser mark needs to be done two times before sputtering.
Therefore, it is objective of the present invention to provide an EMI shielding composition which provides solution to at least two of the above mentioned known problems relating to EMI shielding.